Javadoc

This instance identifier uniquely identifies a specific DataObject in the data tree modeled by YANG.
For Example let's say you were trying to refer to a node in inventory which was modeled in YANG as follows,

You could create an instance identifier as follows to get to a node with id "openflow:1"
InstanceIdentifierBuilder.builder(Nodes.class).child(Node.class, new NodeKey(new NodeId("openflow:1")).build();
This would be the same as using a path like so, "/nodes/node/openflow:1" to refer to the openflow:1 node